Intrinsic Fluorescence Excitation–Emission Matrix Spectral Features of Cottonseed Protein Fractions and the Effects of Denaturants

An overview of effects of gamma radiation on the biological, physicochemical and nutritional parameters of oilseeds and oils

PURPOSE

Gamma irradiation is a non-thermal method for prolonging the shelf-life of foods and it is a possible alternative technology for oilseeds. After harvest, the development of pests and microorganisms, as well as the reactions caused by enzymes reason numerous problems in the oilseeds. Gamma radiation is one of the methods that could inhibit undesired microorganisms, but it can also change the physicochemical and nutritive characteristics of oils.

CONCLUSION

This paper is a brief review of recent publications on the effects of gamma radiation on the biological, physicochemical and nutritional parameters of oils. Overall, gamma radiation is a safe and environmentally friendly method that improves the quality, stability and safety characteristics of oilseeds and oils. In the future, there may also be many health reasons to produce oils using gamma radiation. Investigation of other radiation techniques such as x-rays and electron beams have a good potential once the specific doses that would free them from pests and contaminants have been identified while conserving the benefits without altering their sensory properties.

Vicilin and legumin storage proteins are abundant in water and alkali soluble protein fractions of glandless cottonseed

In this work, we sequentially extracted water (CSPw)- and alkali (CSPa)-soluble protein fractions from glandless cottonseed. SDS-Gel electrophoresis separated CSPw and CSPa to 8 and 14 dominant polypeptide bands (110-10 kDa), respectively. Liquid chromatography-electrospray ionization-tandem mass spectrometry identified peptide fragments from 336 proteins. While the majority of peptides were identified as belonging to vicilin and legumin storage proteins, peptides from other functional and uncharacterized proteins were also detected. Based on the types (unique peptide count) and relative abundance (normalized total ion current) of the polypeptides detected by mass spectrometry, we found lower levels (abundance) and types of legumin isoforms, but higher levels and more fragments of vicilin-like antimicrobial peptides in glandless samples, compared to glanded samples. Differences in peptide fragment patterns of 2S albumin and oleosin were also observed between glandless and glanded protein samples. These differences might be due to the higher extraction recovery of proteins from glandless cottonseed as proteins from glanded cottonseed tend to be associated with gossypol, reducing extraction efficiency. This work enriches the fundamental knowledge of glandless cottonseed protein composition. For practical considerations, this peptide information will be helpful to allow better understanding of the functional and physicochemical properties of glandless cottonseed protein, and improving the potential for food or feed applications.

Characteristics of the interaction mechanisms of xylitol with β-lactoglobulin and β-casein: Amulti-spectral method and docking study

Proteins and functional polyols are essential food ingredients coexisting in the food matrix, and therefore, interactions between them inevitably occur. In this study, the interaction mechanisms of xylitol (XY) with bovine milk β-lactoglobulin (β-LG) and β-casein (β-CN) were studied using multispectral techniques and molecular docking. It was found that XY strongly quenched the intrinsic fluorescence of β-LG and β-CN by static quenching. The values of the binding constants were K_A(β-LG-XY) = 3.369 × 10⁴ L/mol and K_{A(β-CN- XY)} = 7.821 × 10⁴ L/mol, indicating that the binding affinity of XY to β-CN was higher than that for β-LG. Hydrogen bonding and van der Waals forces played a major role in the interactions of XY with β-LG and β-CN, and both interactions were exothermic. Simultaneous fluorescence, three-dimensional fluorescence, and circular dichroism spectroscopy showed that binding of XY did not change the secondary structure of β-LG. However, XY interaction with β-CN led to the conversion of α-helices to random coils and structural loosening. In addition, molecular docking predicted the most likely binding sites of XY in both proteins and the interaction forces involved in binding, confirming the spectroscopic results. This study improves the understanding of the interactions of XY with β-LG and β-CN in functional dairy products and provides a theoretical basis for the addition of XY in a functional milk base.

The ultraviolet-visible absorbance and fluorescence characterization of dissolved organic matter derived from the leaf litter of Populus simonii, Artemisia desertorum, Salix cheilophila, and Populus tomentosa

Dissolved organic matter (DOM) derived from leaf litter plays an important role in maintaining carbon (C) and nitrogen (N) circulation between soils and plants, energy flow, and signaling pathways for plant-microbe interactions of terrestrial ecosystem. In this study, four DOM samples extracted with a 40:1 (v/w) water to sample ratio from the leaf litter of Populus simonii (S1), Artemisia desertorum (S2), Salix cheilophila (S3), and Populus tomentosa (S4) were investigated using the technologies of ultraviolet-visible (UV-Vis) and excitation-emission matrix (EEM) fluorescence spectroscopy. Results showed that the electricity (EC) values of four DOM extracts were significantly different due to the different composition and salt content of each plant. The values of chemical oxygen demand (COD), dissolved organic carbon (DOC), and the sum of values of all peaks' intensities divided by DOC (FI) indicated the higher contents of organic matter in the acid DOM extracts from S1, S2, and S3 (sand-fixing plants) than the neutral DOM extracted from S4. The absorbance shoulder between 250 and 285 nm in the UV-Vis spectra and EEM fluorescence spectra of each sample suggested the presence of many different chromophores such as aromatic or phenolic compounds in plant DOM. According to fluorescence regional integration (FRI) and peak picking results, the content of protein-like materials was higher than that of humic-like substances in DOM from S1, S2, and S3 while the opposite phenomena occurred in DOM from S4. Hence, the physicochemical and fluorescence characterization of DOM extracted from the genus Populus of the family Salicaceae S1 and S4 growing under different edaphic and climatic conditions changed much. The findings would be of great significance to understand the origin, composition, dynamics, and biotransformation of DOM in soils formed in different climatic environments.

A novel Fe2+/persulfate/tannic acid process with strengthened efficacy on enhancing waste activated sludge dewaterability and mechanism insight

As an essential section before final sludge disposal, sludge dewatering has currently been one of the focus issues. In this study, an innovative Fe²⁺/persulfate/tannic acid (TA) process was verified to further strengthen systemic efficacy on enhancing sludge dewaterability, compared with the conventional Fe²⁺/persulfate process. With the efficient TA/Fe²⁺ (molar ratio) of 0.25 added in Fe²⁺ (0.3 mmol/gTS (total solid))/persulfate (0.6 mmol/gTS) process, sludge dewaterability was enhanced remarkably. Capillary suction time, specific resistance to filtration, and water content of dewatered sludge cake were further reduced by 61.5%, 35.3%, and 6.4% than these in Fe²⁺/persulfate. Sludge supernatant viscosity was further reduced by 86.7% due to the more removal of extracellular polymeric substances (EPS). The secondary structure of EPS protein changed apparently and fluorescent components of EPS decreased distinctly. Sludge functional group contents were observed to be lower. TA effectually increased sludge particle size and heightened sludge flocculability, rendering the large and compact aggregations. Moreover, TA accelerated the recovery of Fe²⁺, facilitating persulfate activation to generate more SO₄^·- and ^·OH for EPS disruption and cell lysis in the conditioning system. These findings provided a novel approach based on the Fe²⁺/persulfate process in sludge treatment for desirable dewaterability.

Antioxidant activities of the water-soluble fractions of glandless and glanded cottonseed protein

To promote application of cottonseed protein products in food industry, this work measured antioxidant activities of two water soluble protein samples (Gl-L and Gd-L) isolated in a lab scale from glandless and common glanded cottonseed meal, respectively, and one soluble protein samples (Gd-P) in a pilot scale from glanded cottonseed meal. SDS-gel electrophoresis showed that the distribution patterns of the peptide fragments in Gl-L and Gd-L were similar, but more fragments and higher molecular mass bands were observed in the Gd-P gel image. While Gd-P showed the highest activities, Gl-L and Gd-L exhibited comparable 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radical-scavenging activities in most cases. In contrast, Gd-P showed lower capability of inhibition of linoleic acid autoxidation than Gl-L and Gd-L. It would be of great interest in further research on these protein fractions in food products and processes (such as roasting) involved in the protective effects of food spoilage.

Protein profiling of water and alkali soluble cottonseed protein isolates

Currently, there is only limited knowledge on the protein types and structures of the cottonseed proteins. In this work, water-soluble cottonseed proteins (CSPw) and alkali-soluble cottonseed proteins (CSPa) were sequentially extracted from defatted cottonseed meal. Proteins of the two fractions were separated by 4–20% gradient polyacrylamide gel electrophoresis (SDS-PAGE); There were 7 and 12 polypeptide bands on SDS-PAGE of CSPa and CSPw, respectively. These individual bands were then excised from the gel and subjected to mass spectrometric analysis. There were total 70 polypeptides identified from the proteins of the two cottonseed preparations, with molecular weights ranging from 10 to 381 kDa. While many proteins or their fragments were found in multiple bands, 18 proteins appeared only in one SDS-PAGE band (6 in CSPa, 12 in CSPw). Putative functions of these proteins include storage, transcription/translation, synthesis, energy metabolism, antimicrobial activity, and embryogenesis. Among the most abundant are legumin A (58 kDa), legumin B (59 kDa), vicilin C72 (70 kDa), vicilin GC72-A (71 kDa), and vicilin-like antimicrobial peptides (62 kDa). This work enriched the fundamental knowledge on cottonseed protein composition, and would help in better understanding of the functional and physicochemical properties of cottonseed protein and for enhancing its biotechnological utilization.

Cation-induced coagulation of aquatic plant-derived dissolved organic matter: Investigation by EEM-PARAFAC and FT-IR spectroscopy

Complexation and coagulation of plant-derived dissolved organic matter (DOM) by metal cations are important biogeochemical processes of organic matter in aquatic systems. Thus, coagulation and fractionation of DOM derived from aquatic plants by Ca(II), Al(III), and Fe(III) ions were investigated. Metal ion-induced removal of DOM was determined by analyzing dissolved organic carbon in supernatants after addition of these metal cations individually. After additions of metal ions, both dissolved and coagulated organic fractions were characterized by use of fluorescence excitation emission matrix-parallel factor (EEM-PARAFAC) analysis and Fourier transform infrared (FT-IR) spectroscopy. Addition of Ca(II), Fe(III) or Al(III) resulted in net removal of aquatic plant-derived DOM. Efficiencies of removal of DOM by Fe(III) or Al(III) were greater than that by Ca(II). However, capacities to remove plant-derived DOM by the three metals were less than which had been previously reported for humic materials. Molecular and structural features of plant-derived DOM fractions in associations with metal cations were characterized by changes in fluorescent components and infrared absorption peaks. Both aromatic and carboxylic-like organic matters could be removed by Ca(II), Al(III) or Fe(III) ions. Whereas organic matters containing amides were preferentially removed by Ca(II), and phenolic materials were selectively removed by Fe(III) or Al(III). These observations indicated that plant-derived DOM might have a long-lasting effect on water quality and organisms due to its poor coagulation with metal cations in aquatic ecosystems. Plant-derived DOM is of different character than natural organic matter and it is not advisable to attempt removal through addition of metal salts during treatment of sewage.

Chemical Composition of Defatted Cottonseed and Soy Meal Products

Chemical composition is critical information for product quality and exploration of new use. Hence defatted cottonseed meals from both glanded (with gossypol) and glandless (without gossypol) cotton seeds were separated into water soluble and insoluble fractions, or water soluble, alkali soluble as well as total protein isolates. The contents of gossypol, total protein and amino acids, fiber and carbohydrates, and selected macro and trace elements in these products were determined and compared with each other and with those of soy meal products. Data reported in this work improved our understanding on the chemical composition of different cottonseed meal products that is helpful for more economical utilization of these products. These data would also provide a basic reference for product standards and quality control when the production of the cottonseed meal products comes to pilot and industrial scales.